1. Field of the Invention
The present invention relates to elastomeric seals used in molding apparatus.
2. Background of Related Art
For years, porcelain-cast iron fixtures have been widely used. However, the drawbacks of the porcelain-cast iron and enamelled fixtures have always been their susceptibility to impact damage .and their extreme weight which makes moving and installation of large fixtures such as bathtubs and whirlpools, most difficult. While the porcelain-cast iron fixtures have the advantage of providing a very solid feel and a high weight bearing capability, these drawbacks have made these tubs less attractive to the purchasing public.
Initial attempts by the industry to replace these porcelain-cast iron fixtures, have been to introduce lighter and more resilient component structures, however, this has not been without difficulty. Some of these attempts included thin stainless steel fixtures which were lighter than porcelain-cast iron fixtures, but did not have the solid feel or structural strength required for large articles such as bathtubs and whirlpool tubs. Other attempts included composite structures which had a plastic, hollow feel, and would deform, crack, chip or delaminate when subjected to impact, thermal shock or the weight of a typical bather. One successful solution to the above-mentioned shortcomings and drawbacks of the prior art sanitary fixtures, is disclosed in U.S. Pat. No. 4,664,982 to Genovese, et al., the disclosure of which is incorporated by reference herein. U.S. Pat. No. 4,664,982 to Genovese, et al. discloses a composite enamel steel structure which has the look and feel of the earlier porcelain-cast iron fixtures. The composite structure is light, has high structural strength, and resist delamination, chipping and denting due to impact or thermal shock. The composite enamel steel fixture is formed from a steel shell, which is typically formed from a steel blank by a series of stamping and punching operations. The shell is then enamelled on both its finish and non-finish sides. The enamelling process usually includes heating the steel shell to high temperatures melting the enamel onto the shell surface. This heating and subsequent cooling often results in slight bowing and distortion of the shell. The shell thusly formed is used as a part of a mold to form a layer of reinforced foam plastic by Reaction Injection Molding ("RIM") or by Reinforced Reaction Injection Molding ("RRIM") processing on the non-finished (i.e., underside, of shell).
Commonly assigned U.S. Pat. No. 4,664,092 to Genovese, et al. and patent application Ser. No. 07/400,280 to Kuszaj, et al. both of which are incorporated by reference herein, describe polymeric foam backed enamelled-carbon steel or stainless steel plumbing fixtures that are resistant to chipping, cracking, crazing, delamination or deformation when subjected to impact from either the finish or non-finish side. The use of the aforementioned composite mold structures results in fixtures which have the feel of porcelain-cast iron and enamel fixtures, high impact strength, and resistance to delamination. These composite structures possess excellent physical and mechanical properties as a result of the chemical bonding of the reinforced polymeric layer to the enamelled steel or stainless steel shell.
Another approach was to replace the enamelled-steel shell with a polymeric-cosmetic surface layer and binding that layer directly to a foamed plastic substrate to provide a high impact strength, delamination-resistant structure. This approach is disclosed in commonly assigned U.S. Pat. Nos. 4,844,944 and 4,844,955 both to Graefe, et al., the disclosures of which are incorporated by reference herein. These approaches suffer from the same problems described above with regard to bowing, and warpage of the shell due to the irregularity in the shell from the manufacturing process. Co-pending U.S. patent application Ser. No. 07/458,598 to Marsilio et al. filed on Dec. 29, 1989 now U.S. Pat. No. 5,129,804, describes a molding apparatus which is suitable for molding a layer of reinforced polymeric material to the non-finish side of a shell. The molding apparatus described in this application can be used with any of the shells and polymeric materials which are described in U.S. Pat. Nos. 4,664,982, 4,844,944, 4,844,955 and 4,664,092 and application Ser. Nos. 07/400,280 and 07/458,598 as described above.
Typically, a shell having a finish and a non-finish side is inserted into a female mold receptor forming a cavity between the molding receptacle surface and a non-finish portion of the shell. In order to close the cavity and allow sufficient support to be applied during the molding operation, a male molding portion having a surface which substantially conforms to the finished surface contour of the shell, is urged against the finished side of the shell. A cavity is formed between the molding receptacle and the non-finish side of the shell. The cavity must be sealed around the periphery of the shell to prevent leakage of the foamed polymeric material from the cavity. Accordingly, seals are required which can accommodate variations in the shape of the shells resulting from the manufacturing process used. In one proposed sealing system which may be used, a molding apparatus includes a urethane coating on an undersized male molding portion which matches the finish surface of the shell. This protective urethane coating is molded on the surface of the male molding portion in a space adjacent to the shells finished surface by injecting urethane in the space. The cured polyurethane about the male molding portion forms a surface on the male molding portion which contacts the periphery of the shell and a portion of a molding receptacle, so as to seal off a molding cavity between the non-finish surface of the shell and a surface of the molding receptacle.
This molded sealing system suffers from several significant shortcomings and drawbacks. In particular, the seal is cast as part of the protective urethane surface coating of the male mold portion. It is therefore difficult and expensive to replace. Since such seals typically wear and deteriorate over repeated molding cycles, such sealing systems are not desirable. Also, due to variations in the shape of the shell due to the manufacturing process the shape of the molded seals may vary. Accordingly, it is extremely difficult and often impossible to form an adequately sealed molding cavity with each new shell into which the foamed polymeric material can be introduced under adequate molding pressure. Consequently, the foamed polymeric material flows beyond the seal and often damaging the finished surface of the shell, or adhering to the mold receptor.
In another proposed sealing system used in molding bathtubs, U.S. Pat. No. 2,841,823 discloses a molding apparatus for low pressure compression molding of laminates useful in fabricating large bulky objects such as boats or bathtubs. The mold includes an L-shaped baffle anchored in an upper molding block, extending outwardly and downwardly from the molding block and a lower molding block having a U-shaped channel which faces the L-shaped baffle. An expandable hose is located in the U-shaped channel. To form a seal, compressed air is introduced into the hose, causing it to expand and engage the L-shaped baffle.
This mold sealing system suffers from drawbacks however. In particular, the inflatable hose is only maintained in the U-shaped channel when pressed against the L-shaped baffle. The inflatable hose requires a source of air under pressure to inflate the hose and engage the seal. Also, the inflatable hose may become dislodged from the U-shaped channel when the L-shaped baffle is lifted from the lower molding block.
U.S. Pat. No. 4,732,553 discloses a seal assembly for molding gaskets around the periphery of a window. It also includes fluid filled bladders which are located in both the upper and lower portions of the molding apparatus. Silicone seals rest above the bladders within seal grooves. The inflatable air bladders within the mold seal groove adjust the non-compressible seal to engage the molding cavity. These seals, however, are maintained in the groove by adhesives and therefore are not easily released from the seal groove.
U.S. Pat. Nos. 4,688,752 and 4,854,599 also disclose sealing systems with seals in both the upper and lower cooperating mold sections. These patents describe seals which are retained within a mold seal groove by a clamp. In addition, these patents disclose the use of non-elastomeric fluorocarbon materials such as Teflon making up part of the seal. These non-elastomeric components therefore are unable to accommodate for the inherent distortion present in sanitary fixture shells as discussed above.
In response to the above problems associated with the prior art sealing systems proposed above, an alternative sealing system has been proposed by Applicants. In this proposed sealing system, a seal groove is formed in the male mold portion above the upper flange of the shell and adjacent the cavity form between the non-finished surface of the shell and the female mold, when the molding apparatus is in its closed position. In the seal groove, segments of urethane material are inserted end-to-end to form a seal which is retained in the male mold portion by an overhanging edge projection formed by the protective urethane surface coating on the male mold portion. While such a proposed sealing system provides a seal which can be replaced, it is not done without difficulty. In addition, it suffers from additional shortcomings and drawbacks as well. In particular, the overhanging edge projection of the protective urethane surface coating on the male mold portion, fails to adequately retain the seal in the groove of the male mold portion during demolding operations, and as with other proposed sealing systems described above, it is incapable of establishing an effective seal along all engaging surfaces of the shell and seal due to the inherent variations of the shell due to bowing, warping and distortion of the shell due to manufacturing processes.
In view, therefore, of the shortcomings and drawbacks of the proposed prior art methods, and apparatus for effecting a seal between the shell and molding surface of a mold receptor used to mold products therein, there is a clear need to provide a sealing system that overcomes the above described shortcomings and drawbacks.
Accordingly, it is a primary object of the present invention to provide a seal for a molding receptacle for applying a coating to the underside surface of a sanitary fixture shell, wherein the seal is capable of being releasably retained within a groove contained in either the mold receptor or male molding means.
It is another object of the present invention to provide a seal having at least a first and second layer of elastomeric material which is releasably retained within a seal groove and is capable of accommodating for the shell variations which are inherent to the shell due to the manufacturing process.
It is a further object of the present invention to provide a molding apparatus having an improved seal and retaining means.
It is a further object of the present invention to provide a molding apparatus with a sealing system capable of accommodating variations in sanitary fixture shells due to the manufacturing process of the shells.